1. Related Applications
The invention described herein is related to that described in U.S. patent application Ser. No. 002,268, filed Jan. 12, 1987.
2. Field of the Invention
The present invention relates to a system and method for separating solutes dissolved in and particulates suspended in liquid solvents by diffusion using tuned oscillations.
3. Prior Art
Diffusion has long been employed to separate molecules. Graham [On the law of diffusion of gases. Philosophical Mazagine, Vol. 2, pp. 175-351 (1833)], who first related the molecular diffusion coefficient to the square root of molecular weight, separated gases based upon this principle in the 19th century. Hertz developed a technique based on diffusion to separate gases in a countercurrent system [Z. Physik., Vol. 19, p. 35 (1923); Z. Physik, Vol. 91, p. 810 (1934)].
This technique was extended to liquids by Lange [Z. Naturwiss., Vol. 16, p. 115 (1928); Vol. 17, p. 228 (1928)]. There is evidence that students of Lange expanded on this work and reported their results in papers published in East Germany that are not readily available. East German Patent No. 54339 describes the method of Lange as one involving the enhancement of the diffusion rate by oscillations and regeneration of the solvent by successive distillation and condensation.
Dreyer et al [Die Steigerung des Diffusionstransportes durch Pulsationsdiffusion, Z. Naturforsch. Vol. 23, pp. 498-503 (1968); Die Bestimmung von Diffusionskoeffizienten nach der Pulsationsmethode, Z. Naturforsch. Vol. 24, pp. 883-886 (1969)] describe a system for determining the diffusion coefficients of solutes such as KC, NaCl and CaCl.sub.2 comprising two containers connected by a capillary and a mechanism for creating pulsating oscillations in the liquid contained in the capillary. Although the authors discovered an enhancement of transport by several orders of magnitude across the capillary, they do not describe or suggest utilization of the system to separate solutes contained in a common solvent.
Modified principles of diffusion are used industrially today, especially to separate isotopes of uranium. Diffusion has been used to separate solutes in liquid solution, however, the efficacy of the process is low because the molecular diffusion coefficient of solutes in liquids is about five orders of magnitude smaller than the diffusion coefficient of gases in a gaseous phase, thus reducing the possible yield for a given configuration.
Enhanced diffusion (or dispersion) by oscillatory motion of a fluid finds its roots in the theoretical work by Watson (J. Fluid Mech., 133, p. 233, (1983) who himself expanded on a study by Taylor on the dispersion of solutes in steady laminar flow (Proc. R. Soc. London Ser. A 219, p. 186 (1953). Kurzweg et al recently described the conditions of optimal transport in gases by proper tuning of the experimental variables (Phys. Fluids, Vol. 29, p. 1324 (1986)).
The general principal involved may be described thusly: The oscillation of a fluid column in a tube generates a large surface between the oscillating core and the boundary layer which is essentially not moving. This surface is made available for diffusion. The theory predicts that, under certain conditions, the dispersion coefficient (i.e., the effective diffusion coefficient) is proportional to the square root of oscillation frequency, to the square of the average oscillation amplitude, and to the molecular diffusion coefficient. The diffusion rate (flux) of a solute in an oscillatory system is proportional to the dispersion coefficient, and to the concentration gradient and is dependent on geometry.
It is an object of the present invention to provide a differential diffusion system and method for separating solutes and/or particulates dissolved or suspended in liquid media.